The present invention relates to process control apparatus. More particularly, it relates to improved analog output circuitry for use with a digital computer based process control system.
In the art of industrial process control, there have been provided systems wherein various parameters of a process are measured, compared with a desired value, and a difference there between used to derive a control or output signal. Frequently, both the input, or measured variable signals and the output signals are in the form of analog signals. Most popularly, in multiple loop systems, analog signals are converted to digital signals for processing by a digital computer in accordance with an applied algorithm. Then, the digital output control signals are converted to analog signals for application to the ultimate control element. In the interest of economy and convenience, it is desirable that a plurality of individual output devices be controllable from a single output control board.